Optical bistability (the existence of two distinct, stable output states corresponding to a single input state) has been demonstrated using several techniques e.g. nonlinear dispersion, self-focussing and saturable absorption ("Optical Bistability", C. M. Bowden, M. Ciftan and H. R. Robl, Plenum 1981). To obtain optical bistability, the output of the optical device must be a nonlinear function of some input parameter and sufficient degree of feedback should be incorporated. High light intensities are required in order to achieve the necessary nonlinear behaviour.
Nonlinear absorption in a saturable absorber has been demonstrated as a technique for achieving bistable behaviour in e.g. semiconductor-type lasers--see for example "Bistablility and pulsations in semiconductor lasers with inhomogeneous current injection", C. Harder et al, IEEE J. Quantum Electron, 1982, QE-18 pp